In Pat. No. 3,379,273 entitled "Powerful Sound Impulse Generation Methods and Apparatus", which is assigned to the assignee of the present invention, acoustical impulse generator repeators (now usually called "air guns") are disclosed as operated with gas supplied thereto under high presssure and utilized to generate powerful seismic energy waves in a body of water such as an ocean, sea, lake, river or similar body of water. Such impulses may be conveniently repeated at frequent and accurately timed intervals from one or more air guns, which enable seismic surveys to be made of the conditions and characteristics of the bottom and sub-bottom formations beneath bodies of water. The powerful seismic impulses are adapted for transmission over long distances through the water and through the sub-bottom formations and they enable effective marine seismic surveys to be made.
In Pat. No. 3,779,335 entitled "Confined Liquid Seismic Exploration Methods and Systems", which is assigned to the assignee of the present invention, a compact mobile system is provided which enables seismic surveying and exploration to be carried out at sites having a vast range of surface conditions, for example, on hard ground, soft ground, swampy ground or submerged ground, etc. The system provides powerful seismic impulses which are generated by abruptly releasing high pressure confined gas from one or more air guns into a relatively large volume of confined liquid such as water which in turn is coupled through a diaphragm to the earth to be surveyed. In applications as a land seismic source, the system requires a water supply, and if not available on site, then the water must be transported to the survey site and be carried with the survey vehicles. Also in a freezing environment, steps must be taken to prevent the water in such a land seismic source from freezing. After the discharged gas has been released into the confined liquid, the gas must be separated from the liquid so that the confined liquid again becomes ready for the air gun to be fired. Consequently, as a practical matter, such a confined liquid land seismic source can be fired at a repetition rate no faster than once every eight seconds, and perhaps once every six seconds. Further, the gas-liquid separator is relatively large and extends upwardly giving a relatively high configuration to the confined liquid land source.
In Pat. No. 4,108,271, entitled "Seismic Land Source", which is assigned to the assignee of the present application, is shown a further seismic land source of the confined-liquid type having an outer cage-like frame.